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Fair Value Measurements (Details) (USD $)
In Thousands, unless otherwise specified
Jan. 31, 2013
Jul. 31, 2012
Jan. 31, 2012
Money Market [Member]
     
Cash equivalents measured at fair value $ 19,025 $ 6,581 $ 8,386
Money Market [Member] | Level 1 [Member]
     
Cash equivalents measured at fair value 19,025 6,581 8,386
Commercial Paper [Member]
     
Cash equivalents measured at fair value 10,626 2,441 19,990
Commercial Paper [Member] | Level 2 [Member]
     
Cash equivalents measured at fair value 10,626 2,441 19,990
Certificates of Deposit [Member]
     
Cash equivalents measured at fair value 630 1,260 1,890
Certificates of Deposit [Member] | Level 2 [Member]
     
Cash equivalents measured at fair value $ 630 $ 1,260 $ 1,890